im looking to upgrade to a set of 20inch wheels.. 20*9 et30 and 20*11 et48. is this a good fitment on m5? i know for the rear. im losing about 27mm inner clearence comparing to stock. but can anyone tell me if this will work on f10 m5? thanks. and btw the car is on h&r springs

It sounds like an 11 inch wide wheel will work on the rear with 305 width tires. You may need a spacer to push the wheel out a bit so that all of the extra width isn't negetively impacting the internal clearance.